Select specific properties from include ones in entity framework core

If I understand correctly, you don't want to load the Author entity (because there is no way to load entity with just some non navigation properties populated).

Then the question is why did you specifically add Include(x => x.Author) which is requesting EF to load the Author. Include / ThenInclude methods support eager loading of the related data entities. They are not needed when you use projection (Select).

Interestingly, all EF (Core) versions before EFC 2.0 were ignoring includes for projection type queries. Even the current EFC documentation states that the projection queries fall into Ignored Includes category. However, as you've noticed EFC 2.0 is not ignoring it! So it's either implementation bug and will be fixed, or the documentation bug and will be updated.

For now, simply don't use Include in projection queries. If you execute this:

var result = ctx.News.Select(news => new
{
    news = news,
    Username = news.Author.Username
}).ToList();

the EFC generated SQL query now is as expected:

SELECT [news].[Id], [news].[AuthorID], [news].[ReleaseDate], [news].[Text], [news].[Title], [news.Author].[Username]
FROM [News] AS [news]
INNER JOIN [Authors] AS [news.Author] ON [news].[AuthorID] = [news.Author].[Id] 

Instead of using an anonymous object, you create a NewsDTO class with the properties you want to retrieve (example bellow).

public class NewsDTO
{
    public int Id { get; set; }
    public string Title{ get; set; }
    public string Text { get; set; }
    public DateTime ReleaseDate{ get; set; }
    public string AuthorName { get; set; }
}

Then you can return from your repository layer a method Task<NewsDTO> GetSpecificProperties().

I prefer to use AutoMapper, your code will be cleaner:

return context.NewsTable.ProjectTo<NewsDTO>().ToList()

But you can do using this odd kind

return context.NewsTable
.Include(x => x.Author)
.Select(x => new NewsDTO
        {
            Id = x.Id.,
            Title = x.Title,
            Text = x.Text,
            ReleaseDate = x.ReleaseDate,
            AuthorName = x.Author.Username
        }).ToList();

Obs: Database retrieve data just when you use .ToList(), before this is just IQueryable, so if you have a where clause, prefer use before retrieve data.